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A3: Optimising nitrogen inputs and timing for cereals

Chair: Francis Rayns (Garden Organic)

Managing nitrogen fertility for organic cereals can be a challenge. The session explores ways of ensuring that adequate supplies of nitrogen from inputs and green manures are provided to the crop when needed.

Session summary

Dr Sarah Clarke from ADAS reviewed the general principles and recent research on cereal nitrogen (N) requirements and highlighted the need to match N supply with crop demand in order to optimise yields and minimise losses. This includes the choice of cereal species, i.e. taking into account that wheat is a comparatively N-hungry crop while triticale is more efficient in terms of N use. At (very) low N levels, oats perform best among the cereal species. Dr Clarke also stressed that while conventional cereal breeders have increased wheat yield while maintaining high grain protein, nitrogen use efficiency (NUE) has not been improved through breeding over the last few decades. This issue is currently addressed in a new Defra-funded project which evaluates current and new wheat varieties for NUE (though in conventional conditions). With regard to the timing of N, it was pointed out that two timings are crucial, at tillering and during stem extension, but that crop demand will depend on species, site, weather conditions and many other factors. Readers may want to refer to this paper by ADAS consultant Daniel Kindred et al.:

Steven Briggs from Abacus then reviewed recommendations on the use of manure and stressed that best practice of manure management includes (1) covering the manure and preventing leaching as far as possible; (2) testing the manure composition for N, P, and K in order to gauge the amounts of nutrients going onto the field; (3) ensuring good levels of aeration to combat weed seeds; (4) limiting applications to 170kg N/ha/year; (5) spreading out manure applications over the rotation to avoid excesses and deficiencies; (6) considering the response of N fixing legumes to mulching or manure applications, since N rich material put on grass-clover leys can substantially decrease the amounts of N fixed. Further elements of N management on organic farms include intercropping cereals and legumes; and the use of agroforestry approaches, e.g. by growing N-fixing trees together with arable crops.

Finally, Richard Gantlett from Yatesbury House Farm (Wiltshire) reported an example of N management in a complex 9-year rotation using a system of reduced tillage. Two points were stressed. First, that air is a crucial component of soil and that soil compaction through machinery or animals needs to be addressed by appropriate measures such as loosening. Secondly, an important aim in organic nutrient management is to stabilise nitrogen in the soil.

Discussion points raised:

  • More clarity is needed regarding specifically organic approaches to nitrogen management in cereal production. Is there a major difference in terms of plant health between supplying N in soluble form or through biotic processes?
  • There is also the need to clarify the role of protein content for baking quality of wheat

Individual speaker presentations and abstracts

Sarah Clarke (ADAS): Cereal N agronomy (PDF 224KB)
The key principle in optimising nitrogen inputs to any crop is to match the nutrient supply to the crop demand, both in terms of the amount and timing of nitrogen. This talk will describe the basis for this statement, as well as how nitrogen requirements differ with cereal species, variety, previous cropping and other environmental factors.

Stephen Briggs (Abacus Organic Associates): Organic sources of nitrogen for cereals (PDF 2.3MB)
The presentation considers optimum sources of nitrogen in organic systems, from the perspec-tives of cereal quality, environment and farmer. Based on a broad-reaching review paper written by Abacus, it offers a summary of knowledge and experience in the following areas: nitrogen fixation; nitrogen recycling; the effect of the length of the fertility building phase or ley and the effect of green cover management; type and management of green manures; soil management; the impact of undersowing; seasonality of crops and the impact of manure use and management.

Richard Gantlett (Yatesbury Organic Farm): A farmer perspective on managing N for cereals (PDF 1.4MB)
The rotation on the 600 ha of farmland Yatesbury House Farms in Wiltshire comprises several cereals. On-farm livestock and leguminous pastures are part of the nitrogen management regime, and the farmís team are experimenting with low-till to find a tillage system which optimises fertility maintenance. The presentation introduces Richardís experiences with managing soil nitrogen and identifies what has worked well for cereals.